A printing ink is generally formulated according to strict performance requirements demanded by the intended market application and required properties. Whether formulated for office printing or for production printing, a particular ink is expected to produce images that are robust and durable under stress conditions. In a typical design of a piezoelectric ink jet printing device, the image is applied by jetting appropriately colored inks during four to six rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small translation of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Pigments are a class of colorants useful in a variety of applications such as, for example, paints, plastics and inks, including inkjet printing inks. Dyes have typically been the colorants of choice for inkjet printing inks because they are readily soluble colorants which enable jetting of the ink. Dyes have also offered superior and brilliant color quality with an expansive color gamut for inks, when compared to conventional pigments. However, since dyes are molecularly dissolved in the ink vehicle, they are often susceptible to unwanted interactions that lead to poor ink performance, for example photooxidation from light (will lead to poor lightfastness), dye diffusion from the ink into paper or other substrates (will lead to poor image quality and showthrough), and the ability for the dye to leach into another solvent that makes contact with the image (will lead to poor water-/solvent-fastness). In certain situations, pigments are the better alternative as colorants for inkjet printing inks since they are insoluble and cannot be molecularly dissolved within the ink matrix, and therefore do not experience colorant diffusion. Pigments can also be significantly less expensive than dyes, and so are attractive colorants for use in all printing inks.
Key challenges with using pigments for inkjet inks are their large particle sizes and wide particle size distribution, the combination of which can pose critical problems with reliable jetting of the ink (i.e. inkjet nozzles are easily blocked). Pigments are rarely obtained in the form of single crystal particles, but rather as large aggregates of crystals and with wide distribution of aggregate sizes. The color characteristics of the pigment aggregate can vary widely depending on the aggregate size and crystal morphology. Thus, an ideal colorant that is widely applicable in, for example, inks and toners, is one that possesses the best properties of both dyes and pigments, namely: 1) superior coloristic properties (large color gamut, brilliance, hues, vivid color); 2) color stability and durability (thermal, light, chemical and air-stable colorants); 3) minimal or no colorant migration; 4) processable colorants (easy to disperse and stabilize in a matrix); and 5) inexpensive material cost. Thus, there is a need addressed by embodiments of the present invention, for smaller nano-sized pigment particles that minimize or avoid the problems associated with conventional larger-sized pigment particles. There further remains a need for processes for making and using such improved nano-sized pigment particles as colorant materials. The present nanosized pigment particles are useful in, for example, paints, coatings and inks (e.g., inkjet printing inks) and other compositions where pigments can be used such as plastics, optoelectronic imaging components, photographic components, and cosmetics among others.
Microreactors have been defined as “Microsystems fabricated, at least partially, by methods of microtechnology and precision engineering. Fluid channels range from 1 um (nanoreactors) to 1 mm (minireactors).” See Microreactors, Ehrfeld, Hessel & Lowe 2000, and W. Ehrfeld et al., “Microreactors—New Technology for Modern Chemistry, 1st Edition, Wiley-VCH, Weinheim, 5-11 (2001), the entire disclosures of which are incorporated herein by reference. Typical microreactors consist of miniaturized channels, often imbedded in a flat surface referred to as the “chip.” These flat surfaces can be glass plates or plates of metals such as stainless steel or Hastelloy. Microreactors have proven to be highly valuable tools in organic chemistry due to their wide flexibility of operating conditions with efficient heat transfer, optimized mixing, and high reaction control. Advantages of a microreactor over more conventional batch reactions include: faster efficient mixing, selectivity enhanced-side products and secondary reactions reduced, higher yields and purities, extreme reaction conditions, time and cost savings, and increased surface area to volume ratio that results in good mass and heat transfer. Microreactors are particularly useful for rapid optimization, screening different reaction conditions, catalysts, ligands, bases, and solvents; mechanistic studies; cost effective industrial scale up; and rapid screening for new pharmaceuticals. Although microreactors have distinct advantages over conventional batch reaction techniques, microreactor chemistry also has its own shortcomings. For example, microreactors generally do not tolerate particulate matter well, often clogging.
Few examples exist where micro reaction technology has been applied to the production of suspensions containing solid materials. This is on account of the high potential for blockage of the micro channels that form these micro devices (less than 1 mm). Some example do exist where custom fabricated microreactors can be applied to the synthesis of solid materials (pigments). See, for example, U.S. Pat. Nos. 6,437,104 B1, 6,469,147 B2, and 6,723,138 B2. Custom made micro fluidic devices have also been applied for the production of fine pigments. See, for example, U.S. Patent Publications Nos. 2005/0109240 A1 and 2008/0078305 A1. These references have generally avoided the clogging of microreactor channels by either ensuring turbulent flow conditions or by designing simplified microfluidic devices with a limited number of passes (once through) and therefore a limited number of bends. Neither of these approaches is however convenient for the general production of materials in microreactors. Turbulent flow conditions require that fluids be pumped through the microreactor at high flowrates and this leads to high pressure drops through the system that increase the required pump delivery pressures. Secondly high flowrates may be detrimental to the synthesis of the desired material as the material is degraded by flow induced shear during the synthesis. Simplified microfluidic devices with a single straight through pass are also not convenient as such devices offer limited mixing efficiencies and therefore low yields. Furthermore the productivity of such devices is restricted by the limited residence times they offer. Low flowrates in the range of μL/min are generally used to make materials with these devices. Such flowrates are not practical for the large scale production of solid materials. Microreactors with flow rates that are 3 to 6 orders of magnitude higher are more practical (mL/min to L/min). A more desirable microreactor process for solid material synthesis, and in our specific case pigment synthesis, would be one that offers a wide range of possible residence times through the use of multiple bends and passes internal to the microreactor and under flow conditions that are laminar without clogging. No such process has been reported. We report here a microreactor process that produces solid pigment particles under laminar flow conditions and at high flowrates by limiting the growth of the formed pigment particles to the nanometer range and thus preventing clogging. This process leads to a production rate of the desired nanopigment and permits good control of the reaction conditions as compared to the conventional batch process.
The following documents provide background information:
U.S. Patent Application Publication No. 2008/0078305 A1 describes two or more solutions comprising an organic pigment solution in which an organic pigment is dissolved in a good solvent, and a poor solvent compatible with the good solvent, or a solution of the poor solvent are allowed to flow through a microchannel in a non-laminar state; and organic pigment fine particles are deposited from the organic pigment solution in a course of flowing through the microchannel by changing the solubility of the organic pigment solution with the poor solvent or the solution of the poor solvent. As a result, nanometer-scale monodisperse organic pigment fine particles can be produced in a stable manner.
U.S. Patent Application Publication No. 2006/0194897 A1 describes a pigment dispersion that can be suitably used as a coloring material for inks, especially inks for ink-jet recording, comprising a colored pigment in primary particles dispersed stably in a liquid medium, and a process for producing the pigment dispersion. A pigment dispersion comprising a colored pigment that is substantially of a primary particle maintaining type and is dispersed in a liquid medium, a process for producing the pigment dispersion, and an ink and recorded image using the pigment dispersion.
U.S. Patent Application Publication No. 2003/0164118 A1 describes a process for conditioning organic pigments by introducing a liquid prepigment suspension into a miniaturized continuous reactor and thermally treating therein.
U.S. Patent Application Publication No. 2003/0158410 A1 describes a process for preparing diketopyrrolopyrrole pigments comprises conducting the elementary steps of pigment synthesis (reaction and hydrolysis) in a miniaturized continuous reactor.
U.S. Patent Application Publication No. 2007/0289500 A1 describes a method of producing a dispersion of a pigment, comprising: bringing a solution in which an organic pigment is dissolved, and an aqueous medium, into contact with each other in a channel having an equivalent diameter of 1 mm or less, thereby making the pigment into a fine particle thereof, wherein at least one of the solution and the aqueous medium comprises at least one anionic dispersing agent.
U.S. Patent Application Publication No. 2007/0213516 A1 describes a process for producing high-purity azo colorants is characterized in that (a) at least the azo coupling is carried out in a micro-reactor, (b) the azo-dye produced in the micro-reactor is brought into intimate contact with an organic solvent from the group of the C3-C6 alcohols, the C4-C10 ether alcohols and the halogenated aromatics at a temperature from 0 to 60° C., and (c) the azo dye produced in the micro-reactor is subjected to membrane purification in an aqueous or solvent-containing suspension.
WO 2006/132443 A1 describes a method of producing organic pigment fine particles, wherein when producing organic pigment fine particles by allowing two or more solutions at least one of which is an organic pigment solution in which an organic pigment is dissolved to flow through a microchannel, the organic pigment solution flows through the microchannel in a non-laminar state. Accordingly, the contact area of solutions per unit time can be increased and the length of diffusion mixing can be shortened, and thus instantaneous mixing of solutions becomes possible. As a result, nanometer-scale monodisperse organic pigment fine particles can be produced in a stable manner.
U.S. Pat. No. 7,160,380 describes a method of producing a fine particle of an organic pigment, containing the steps of: flowing a solution of an organic pigment dissolved in an alkaline or acidic aqueous medium, through a channel which provides a laminar flow; and changing a pH of the solution in the course of the laminar flow.
U.S. Pat. No. 7,262,284 describes a method for the production of a diazo pigment, or a mixture of diazo pigments, according to formula (1) of the specification by azo coupling, wherein the azo coupling product is subjected to a finish in an organic solvent or in an aqueous organic solvent with a neutral or alkaline pH.
U.S. Patent Application Publication No. 2002/0058794 A1 describes a process for preparing disazo condensation pigments by diazotization of an aromatic amine, azo coupling with a coupling component to form an azocarboxylic acid or azodicarboxylic acid, formation of an azocarbonyl chloride or azodicarbonyl dichloride and condensation of the azocarbonyl chloride with an aromatic diamine or of the azodicarbonyl dichloride with an aromatic amine comprises effecting the acyl chloride formation and/or the condensation and optionally the diazotization and optionally the azo coupling in a microreactor.
U.S. Patent Application Publication No. 2001/0029294 A1 describes azo colorants that are prepared by conducting the diazotization of aromatic or heteroaromatic amines or the azo coupling reaction or the diazotization and the azo coupling reaction in a microreactor.
Hideki Maeta et al., “New Synthetic Method of Organic Pigment Nano Particle by Micro Reactor System,” in an abstract available on the internet, describes a new synthetic method of an organic pigment nanoparticle was realized by micro reactor. A flowing solution of an organic pigment, which dissolved in an alkaline aqueous organic solvent, mixed with a precipitation medium in a micro channel. Two types of micro reactor can be applied efficiently on this build-up procedure without blockage of the channel. The clear dispersion was extremely stable and had narrow size distribution, which were the features, difficult to realize by the conventional pulverizing method (breakdown procedure). These results proved the effectiveness of this process on micro reactor system.
U.S. Patent Application Publication No. 2005/0109240 describes a method of producing a fine particle of an organic pigment, containing the steps of: flowing a solution of an organic pigment dissolved in an alkaline or acidic aqueous medium, through a channel which provides a laminar flow; and changing a pH of the solution in the course of the laminar flow.
WO 2006/132443 A1 describes a method of producing organic pigment fine particles by allowing two or more solutions, at least one of which is an organic pigment solution in which an organic pigment is dissolved, to flow through a microchannel, the organic pigment solution flows through the microchannel in a non-laminar state. Accordingly, the contact area of solutions per unit time can be increased and the length of diffusion mixing can be shortened, and thus instantaneous mixing of solutions becomes possible. As a result, nanometer-scale monodisperse organic pigment fine particles can be produced in a stable manner.
K. Balakrishnan et al., “Effect of Side-Chain Substituents on Self-Assembly of Perylene Diimide Molecules: Morphology Control,” J. Am. Chem. Soc., vol. 128, p. 7390-98 (2006) describes the use of covalently-linked aliphatic side-chain substituents that were functionalized onto perylene diimide molecules so as to modulate the self-assembly of molecules and generate distinct nanoparticle morphologies (nano-belts to nano-spheres), which in turn impacted the electronic properties of the material. The side-chain substituents studied were linear dodecyl chain, and a long branched nonyldecyl chain, the latter substituent leading to the more compact, spherical nanoparticle.
U.S. Patent Application Publication No. 2003/0199608 discloses a functional material comprising fine coloring particles having an average primary particle diameter of 1 to 50 nm in a dried state, and having a BET specific surface area value of 30 to 500 m2/g and a light transmittance of not less than 80%. The functional material composed of fine coloring particles, exhibits not only an excellent transparency but also a high tinting strength and a clear hue.
U.S. Pat. No. 6,537,364 discloses a process for the fine division of pigments which comprises dissolving coarsely crystalline crude pigments in a solvent and precipitating them with a liquid precipitation medium by spraying the pigment solution and the precipitation medium through nozzles to a point of conjoint collision in a reactor chamber enclosed by a housing in a microjet reactor, a gas or an evaporating liquid being passed into the reactor chamber through an opening in the housing for the purpose of maintaining a gas atmosphere in the reactor chamber, and the resulting pigment suspension and the gas or the evaporated liquid being removed from the reactor through a further opening in the housing by means of overpressure on the gas entry side or underpressure on the product and gas exit side.
U.S. Pat. No. 5,679,138 discloses a process for making ink jet inks, comprising the steps of: (A) providing an organic pigment dispersion containing a pigment, a carrier for the pigment and a dispersant; (B) mixing the pigment dispersion with rigid milling media having an average particle size less than 100 μm; (C) introducing the mixture of step (B) into a high speed mill; (D) milling the mixture from step (C) until a pigment particle size distribution is obtained wherein 90% by weight of the pigment particles have a size less than 100 nanometers (nm); (E) separating the milling media from the mixture milled in step (D); and (F) diluting the mixture from step (E) to obtain an ink jet ink having a pigment concentration suitable for ink jet printers.
Japanese Patent Application Publications Nos. JP 2007023168 and JP 2007023169 discloses providing a pigment dispersion compound excellent in dispersibility and flowability used for the color filter which has high contrast and weatherability. The solution of the organic material, for example, the organic pigment, dissolved in a good solvent under the existence of alkali soluble binder (A) which has an acidic group, and a poor solvent which makes the phase change to the solvent are mixed. The pigment nanoparticles dispersed compound re-decentralized in the organic solvent containing the alkali soluble binder (B) which concentrates the organic pigment nanoparticles which formed the organic pigment as the particles of particle size less than 1 μm, and further has the acidic group.
Kazuyuki Hayashi et al., “Uniformed nano-downsizing of organic pigments through core-shell structuring,” Journal of Materials Chemistry, 17(6), 527-530 (2007) discloses that mechanical dry milling of organic pigments in the presence of mono-dispersed silica nanoparticles gave core-shell hybrid pigments with uniform size and shape reflecting those of the inorganic particles, in striking contrast to conventional milling as a breakdown process, which results in limited size reduction and wide size distribution.
U.S. Patent Application Publication No. 2007/0012221 describes a method of producing an organic pigment dispersion liquid, which has the steps of: providing an alkaline or acidic solution with an organic pigment dissolved therein and an aqueous medium, wherein a polymerizable compound is contained in at least one of the organic pigment solution and the aqueous medium; mixing the organic pigment solution and the aqueous medium; and thereby forming the pigment as fine particles; then polymerizing the polymerizable compound to form a polymer immobile from the pigment fine particles.
The appropriate components and process aspects of each of the foregoing may be selected for the present disclosure in embodiments thereof, and the entire disclosure of the above-mentioned references are totally incorporated herein by reference.